Using a single sound card for FreeDV

[Mooneer Salem]

Hi all,

We received a feature request recently regarding updating the FreeDV client application to allow configuration using a single sound card. The way that this would work is that you'd tell it that one of the channels would point to the radio and the other would be for analog audio (i.e. your speaker/microphone or headset), Currently, the FreeDV application requires two separate sound cards to fully enable transmit capability (one for your radio interface and one for analog audio). 

Anyway, I have some questions:

1. How many users would like such a feature? So far I've only heard about it from the discussion thread (https://github.com/drowe67/freedv-gui/discussions/374) so I'm not sure how much demand there is.

2. How common is being able to select audio channels (not just sound devices) among other ham radio applications? I know for sure that WSJT-X can, for example.

3. Is this something that can be already be done using other means? For instance, it may be possible via PulseAudio on Linux but I'm not 100% sure on that (and probably won't help people on other platforms).

Thanks,

-Mooneer K6AQ

[ma...@flyfast.net]

I’m curious on how this would work? While playback devices typically have stereo, recording devices don’t. Or does someone have a (non-professional) stereo input? I have several professional sound cards that have up to 8 channels of bidirectional capability. In looking just now, (wsjtx, js8call, varac) none support identification beyond “playback/recording” thus I can’t choose the channel. Typically I’d run an ASIO or WDM aware application for this. I certainly wouldn’t complain about the ability, but I don’t use these devices for amateur use.

 

Matt

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[ma...@flyfast.net]

I should have read the post first….

 

I don’t see how the OP would accomplish the switching…. FreeDV is taking an input and passing it in real time to an output. Of course, if the sound device is full duplex, I could see where the switching could work, but it seems kludgy to me.

 

Matt

 

From: digita...@googlegroups.com <digita...@googlegroups.com> On Behalf Of Mooneer Salem
Sent: Tuesday, May 16, 2023 5:02 PM
To: digita...@googlegroups.com
Subject: [digitalvoice] Using a single sound card for FreeDV

 

Hi all,

--

[Bob Bristow]

Why waste so much development time to avoid using a $5 USB  sound card?

Bob

Vk6pop

--

[Keith Prosser]

hi Matt have you tried using virtual audio cable, I use this to receive off a sdr and listen to freedv on a laptop.

Kieth GW8TRO 

[Mooneer Salem]

Hi Matt,

I'm actually not sure on how common sound devices with two input channels are, but I did double-check the version of WSJT-X on my laptop and it does seem I can select audio channels (see attached screenshot). I can't comment on any of the others, though, and it may depend on the radio/interface you're using too.

Thanks,

-Mooneer K6AQ

To view this discussion on the web visit https://groups.google.com/d/msgid/digitalvoice/002001d98849%240b32d090%24219871b0%24%40flyfast.net.

[John D. Hays]

Many of these sound cards have crosstalk issues. You end up having output coming back in the input. This can really mess with modems. 

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[Stuart Longland]

On 17/5/23 08:52, ma...@flyfast.net wrote:
> I’m curious on how this would work? While playback devices typically
> have stereo, recording devices don’t.

I've got two laptops that have stereo recording inputs.

One is a 2008-era Apple MacBook, it doesn't have a microphone port but
instead, a stereo line-in socket.

The other is my current laptop (Panasonic CF-53) -- but the catch there
is to enable the microphone input to be a stereo line-in, the sound card
profiles require that I direct stereo audio output to HDMI. I know of
very few radio transceivers that can pick up transmit audio from a HDMI
stream.
--
Stuart Longland (aka Redhatter, VK4MSL)

I haven't lost my mind...
...it's backed up on a tape somewhere.

[Tony Langdon]

On 17/5/23 8:02 am, Mooneer Salem wrote:
>
> Anyway, I have some questions:
>
> 1. How many users would like such a feature? So far I've only heard
> about it from the discussion thread
> (https://github.com/drowe67/freedv-gui/discussions/374) so I'm not sure
> how much demand there is.

It's something I might use, when using a conventional radio interface
with soundcard audio feed. Would save hunting around for a USB audio
device and having to make do with headphones. However, when using my
FT-818 that's not an issue, because with that radio, I use the SCU-17
interface, which has a USB sound device.

> 2. How common is being able to select audio channels (not just sound
> devices) among other ham radio applications? I know for sure that WSJT-X
> can, for example.

Some server side applications (thelinkbox, SvxLink) can do separate
channels as well, to use each one for a different radio.

>
> 3. Is this something that can be already be done using other means? For
> instance, it may be possible via PulseAudio on Linux but I'm not 100%
> sure on that (and probably won't help people on other platforms).

As I use Windows for end user applications, I think "probably not",
unless I can do some funky magic with VoiceMeeter and multiple virtual
audio devices.

--
73 de Tony VK3JED/VK3IRL
http://vkradio.com

[Stuart Longland]

On 17/5/23 17:29, Tony Langdon wrote:
>> 2. How common is being able to select audio channels (not just sound
>> devices) among other ham radio applications? I know for sure that WSJT-X
>> can, for example.
> Some server side applications (thelinkbox, SvxLink) can do separate
> channels as well, to use each one for a different radio.

`direwolf` too. One possible use case would be with the UDRC or DRAWS:
analogue headset into one of the ports and radio into the other.

However, USB audio interface, USB headset, or even Bluetooth are viable
alternatives that require zero changes to FreeDV.

[KT4WO]

"Why waste so much development time to avoid using a $5 USB sound card?"

AGREE!!

And I would bet this would almost NEVER be used.

KT4WO

[Boudewijn (Bob) Tenty]

+1

Bob VE3TOK

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-- 
There is nothing permanent except change
 
-Heraclitus

[Pierre Martel]

The only nice use I would see is if someone can use a SBC without integrated audio, it would be possible to use a single  card and a hardware switching system that would follow the ptt switch in the software to switch the microphone input between the radio output (in receive mode) and the analog mike the ham will use. The stereo output would either feed a small speaker for the decoded/encoded audio and the other channel could send a tone when in tx so that the switching circuit could detect when in tx and put the ptt switching circuit in ptt mode and mute the audio signal to the speaker so not to ear the transmitted modem signal. Kind of a vox system. Why have a full duplex audio system when it is not needed. We either receive and decode or tx and encode.